1. Field of the Invention
The present invention relates to an improvement in a case for containing an electrical instrument such as a micro-speaker installed in a mobile communication instrument of a mobile phone and so on.
2. Description of the Prior Art
Conventionally, for example, a speaker used widely in a mobile communication instrument such as a mobile phone, a PDA (Personal Digital Assistant), a pager, a small game machine and so on comprises a case and an electrical instrument such as a sound generator, contained in the case.
Because such a micro-speaker is formed into a small chip similarly to the other electronic parts and practiced in a surface-mounting type capable of soldering only on one surface of a circuit substrate so as to be adapted to mount the parts with a high density mounting on the circuit substrate of the mobile communication instrument, it is required that the case is formed in a thinned type and configured to contain efficiently and inexpensively the electrical instrument.
A case in such a conventional micro-speaker of the surface-mounting type has a frame 1 and a cover member 2 attached to the frame 1, as shown in FIG. 6. When the cover member 2 is attached to the frame 1, a sound generator (not shown), which is an electrical instrument, is contained in a space 3 between the cover member 2 and the frame 1. The frame 1 and the cover member 2 form the case by inserting an outer peripheral surface 4 of the frame in an inner peripheral surface 5 of the cover member 2.
In this case, an adhesive is applied on at least one of an inner peripheral surface of the cover member 2 and the outer peripheral surface 4 of the frame 1 and then the adhesive is hardened by means of heating to fix the cover member 2 to the frame 1.
However, in the conventional case as described above, because there are variations in an amount of the adhesive applied between the cover member 2 and the frame 1, there are also generated variations in a force of fixing, in other words, a force of combining, the cover member and frame. Consequently, the strength of the case in a drop impact is insufficient and the cover member 2 cannot be mounted properly on the frame 1 and therefore a height of an assembly of the cover member 2 and frame 1 tends to become uneven.